Image forming apparatus

ABSTRACT

An image forming apparatus includes a reading portion for reading a shape of a first sheet, said reading portion having a function of reading a second sheet carrying an original image; an image forming portion for forming a toner image corresponding to the original image read by said reading portion; a fixing portion for fixing the toner image formed by said image forming portion; and a controller for controlling a fixing condition of said fixing portion in accordance with the shape of the first sheet read by said reading portion.

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to an image forming apparatus for forminga toner image (image formed of toner) on a sheet of recording medium(which hereafter may be referred to simply as recording medium).

In the field of an image forming apparatus, it has been proposed to setthe conditions under which image formation processes are controlled,according to the shape and thickness of the recording medium to be usedfor image formation. Ordinarily, the size and thickness of the recordingmedium to be used for image formation are selected by an operatorthrough a controlling portion, or the like, of an image formingapparatus. Then, the conditions under which the image formationprocesses are controlled are automatically adjusted by the controlportion of an image forming apparatus, according to the selected sizeand thickness of the recording medium.

According to Japanese Laid-open Patent Application No. 2003-149887, therecording medium conveyance passage of the image forming apparatus isprovided with an additional member for detecting the thickness ofrecording medium, and the conditions under which image formationprocesses are carried out are adjusted according to the detectedthickness of the recording medium. According to Japanese Laid-openPatent Application No. 2006-30629, the width and length of a sheet ofrecording medium which is unusual in shape are read by an image readingmeans for obtaining the information of an image to be formed.

However, what kinds of image formation processes are controlled, andconcrete methods for controlling an image forming apparatus in imageformation process according to the shape and thickness of the recordingmedium, have not been addressed in the past. In the past, therefore, allthat could be done to deal with a sheet of recording medium which doesnot have an ordinary rectangular shape was to apply image formationconditions such as those described regarding the conventional art, tothe unusually shaped sheet of recording medium. Thus, it has beendifficult to obtain the optimal products.

More concretely, it is possible that an image forming apparatus willbecome unstable in fixation temperature and/or fixation pressure, andtherefore, the apparatus will output toner images which are nonuniformin glossiness.

SUMMARY OF THE INVENTION

The present invention was made in consideration of such a situation asthose described above. Thus, the primary object of the present inventionis to provide an image forming apparatus which can easily set infixation condition according to the characteristics (shape and size) ofa sheet of recording medium, even if the sheet does not have an ordinaryrectangular shape.

According to an aspect of the present invention, there is provided animage forming apparatus comprising a reading portion configured to reada shape of a first sheet, said reading portion having a function ofreading a second sheet carrying an original image; an image formingportion configured to form a toner image corresponding to the originalimage read by said reading portion; a fixing portion configured to fixthe toner image formed by said image forming portion; and a controllerconfigured to control a fixing condition of said fixing portion inaccordance with the shape of the first sheet read by said readingportion.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of the image forming apparatus inthe first embodiment of the present invention, and is for describing thestructure of the apparatus.

FIG. 2 is a schematic sectional view of the essential portion of thefixing apparatus in the first embodiment, and is for describing thestructure of the essential portion.

FIG. 3 is an enlarged schematic cross-sectional view of the heater ofthe fixing apparatus in the first embodiment.

FIG. 4 is a schematic drawing of the electric power supply system forthe heater.

FIG. 5 is a schematic sectional view of the original image readingportion of the image forming apparatus, and is for describing thestructure of the portion.

FIG. 6 is a block diagram of the control system of the image formingapparatus.

FIG. 7 is a schematic drawing of a combination of the heater of thefixing apparatus in the first embodiment, and an unusually shaped sheetof recording medium, which is for describing the first embodiment.

FIG. 8 is a flowchart of the operational sequence of the image formingapparatus in the first embodiment.

Parts (a)-(e) of FIG. 9 are a collection of various examples of acombination of instructions (prompts) and buttons displayable across thescreen portion of the control panel of the image forming apparatus inthe first embodiment.

FIG. 10 is a drawing for describing the relationship between the amountof the secondary transfer current and the length of time elapsed afterthe entrance of an unusually shaped sheet of recording medium into thefixing apparatus in the first embodiment.

FIG. 11 is a drawing for describing the relationship between the amountof the pressure applied to the fixation nip and the length of elapsedtime after the entrance of the unusually shaped sheet of recordingmedium into the fixation nip.

FIG. 12 is a schematic sectional view of the fixing apparatus in thesecond embodiment of the present invention, and is for describing thestructure of the apparatus.

FIG. 13 is a schematic drawing of an envelope as an unusually shapedrecording medium which can be accommodated by the image formingapparatus in the third embodiment of the present invention.

FIG. 14 is a flowchart of the operational sequence of the image formingapparatus in the third embodiment.

Parts (a)-(h) of FIG. 15 are a collection of various examples of acombination of instructions (prompts) and buttons displayable across thescreen portion of the control panel of the image forming apparatus inthe third embodiment.

FIG. 16 is a flowchart of the subordinate operational sequence of one ofthe primary operational sequence of the printing portion of the imageforming apparatus in the third embodiment.

DESCRIPTION OF THE EMBODIMENTS Embodiment 1

FIG. 1 is a schematic sectional view of the image forming apparatus inthis embodiment of the present invention. It is for describing thestructure of the apparatus. This image forming apparatus is of theso-called intermediary transfer type, and uses an electrophotographicimage forming method. Further, it is of the so-called tandem type, andis a digital color copying machine. Generally speaking, this imageforming apparatus has:

1) Original image reading portion 51 (original image reading means) forreading the original image to obtain the information (first information)of the image to be formed;

2) Printing portion 50 (image forming portion; image forming means) forforming a toner image on a sheet of recording medium;

3) Fixing apparatus 16 (fixing means) for applying a combination of apreset amount of heat and a preset amount of pressure to the sheet ofrecording medium and the toner image thereon to fix the toner image tothe sheet;

4) Control panel 20 (user interface) to be used by a user to control theimage forming apparatus; and

5) Control portion 200 (controlling means).

The printing portion 50 has: an image bearing member 8 on which a tonerimage is formed based on the above-mentioned first information(information of image to be formed); and a transferring means 13 fortransferring the toner image formed on the image bearing member 8, ontoa sheet S of recording medium, with the use of a preset amount ofvoltage or electric current.

A job, which is a combination of the data of the image to be formed, andthe information of the recording medium to be used for the job, isinputted into the control portion 200 from an external device 300 suchas the original image reading portion 51, a PC (personal computer), animage reader, a network, a facsimileing machine, the control panel 202,etc. As the job is inputted, the printing portion 50 carries out animage forming operation which matches the inputted job, to output afull-color, or monochromatic print.

The control portion 202 is in charge of the overall operation of theimage forming apparatus. That is, it controls the conditions under whichthe printing portion 50 forms an image. The information of the originalread by the original image reading portion 51 is inputted into thecontrol portion 200 from the original image reading portion 51. Thesetting and instruction regarding the image formation are inputted intothe control portion 200 by a user (operator) through the control panel202. Further, the information regarding the condition of the imageforming apparatus, and related operational instructions are offered tothe user across the screen of the control panel 202 from the controlportion 200.

The control panel 202 is provided with an inputting portion 202A and adisplaying portion 202B (display: UI screen: informing means). Theinputting portion 202A is provided with various keys, such as a mainswitch, a group of numerical keys for inputting numerical values, aprint-start button, a print-stop key, and an economy mode button. Thedisplaying portion 202B is a liquid crystal screen (liquid crystal touchpanel), across which not only various information such as types of sheetof recording medium usable by the image forming apparatus, but also,images of various buttons to be used to control the image formingapparatus, are displayed. The information regarding the variousoperations to be carried out by the image forming apparatus, and also,the information regarding the sheet of recording medium to be used forimage formation, can also be inputted with the use of the buttonsdisplayed across the displaying portion.

The information regarding the various settings for the operations to becarried out by the image forming apparatus, and the informationregarding the recording medium, are inputted into the control portion200 also from the external devices 300 such as a PC.

Here, a “sheet” is a sheet of recording medium (media: material) acrosswhich a toner image can be formed by the printing portion 50. As a“sheet”, a sheet of ordinary paper which is ordinary or unusual inshape, a sheet of thin paper, a sheet of cardstock, a sheet of highquality paper, an envelope, a post card, a seal, a label, a sheet ofresinous substance, a sheet of OHP film, a sheet of printing paper, aformatted sheet of paper, etc., can be listed, for example. Hereafter, a“sheet” may be referred to simply as recording medium, or recordingmaterial.

A “job (image formation job)” means an image formation instruction whichincludes the information such as the image data, preset type, basisweight, size, and shape of recording medium, preset post image formationprocess, etc.

(Printing Portion)

The printing portion 50 has four image forming portions UY, UM, UC andUK which form yellow (Y), magenta (M), cyan (C) and black (K) tonerimages, respectively. These image forming portions are aligned in tandemin the left-to-right direction with reference to FIG. 1. The imageforming apparatus is provided with an intermediary transfer belt unit 7,which is on the bottom side of the combination of these image formingportions.

The four image forming portions are roughly the same in structure,although they are different in the color of the toner (developer) theyuse. They use an electrophotographic process. Each image forming portionhas: an electrophotographic photosensitive drum 1 (which hereafter maybe referred to simply as drum) as the first image bearing member; acharge roller 1; an exposing apparatus 3 (laser scanner); a developingdevice 4; a primary transfer roller 5, and a drum cleaner 6. By the way,for the purpose of preventing FIG. 1 from appearing unnecessarycomplicated, the referential codes for these components, members,portions, etc. in the image forming portions UM, UC and UK are notshown; only the referential codes for the components, member, portions,etc, in the image forming portion UY are shown in FIG. 1. Further, theelectrophotographic image formation process used by each image formingportion, and the image forming operation of each image forming portion,are well-known, and therefore, are not described here.

The four toner images, different in color, which are on the four drums 1in the four image forming portions U, one for one, are transferred inlayers (primary transfer) in a preset manner, onto an intermediarytransfer belt 8 (intermediary transferring member: which hereafter willbe referred to as transfer belt), as the second image bearing member, ofthe intermediary transfer belt unit 7, which is being circularly moved.Consequently, an unfixed full-color toner image is formed on thetransfer belt 8, of the four monochromatic toner images, that is, yellow(Y), magenta (M), cyan (C) and black (K) toner images.

Meanwhile, multiple sheets S of recording medium (transfer medium) setin a recording medium holding portion 10 (sheet feeding portion:recording medium setting portion) are fed one by one into the mainassembly of the image forming apparatus. Then, each sheet S of recordingmedium is introduced into the secondary transfer nip 14 with a presetcontrol timing, through a recording medium conveyance passage 12. Then,it is conveyed through the secondary transfer nip 14. While the sheet Sis conveyed through the secondary transfer nip 14, the layered fourtoner images, different in color, on the transfer belt 8 are transferredtogether (secondary transfer) onto the sheet S. A secondary transferroller 13 (transferring means) is kept pressed against the backup roller9 of the intermediary transfer belt unit 7, with the presence of thetransfer belt 8 between the two rollers 13 and 9. The area of contactbetween the transfer belt 8 and secondary transfer roller 13 is thesecondary transfer nip 14.

As soon as the sheet S of recording medium moves through the secondarytransfer nip 14, the sheet S is separated from the transfer belt 8.Then, the sheet S, which is bearing the toner image T which has justbeen transferred onto the sheet S, is introduced into a fixing apparatus16 (fixing means) through a recording medium conveyance passage 15, andis conveyed through the fixing apparatus 16. As the sheet S is conveyedthrough the fixing apparatus 16, the toner image T is fixed to the sheetS by a combination of heat and pressure (preset amount of heat andpresent amount of pressure) applied to the sheet S and the toner image Tthereon, by the fixing apparatus 16. More specifically, as the unfixedfour toner images, different in color, are subjected to the combinationof heat and pressure applied thereon, they melt and mix. Then, as theycool down, they become fixed to the sheet S, yielding a permanentfull-color image. Then, the sheet S is outputted as a finished product(print) from the fixing apparatus 16. The transfer residual toner, orthe toner remaining on the transfer belt 8 after the secondary transferof the toner image T onto the sheet S, is removed from the surface ofthe belt 8 by the belt cleaner 17.

(Toner)

Toner is made by mixing bonding resin such as styrene resin, polyesterresin, or the like, coloring agent such as carbon black, magnetite, dye,pigment, or the like, releasing agent such as wax, charge control agent,or the like, at a proper ratio. Nonmagnetic toner such as the onedescribed above can be manufactured with the use of such a method aspulverization and polymerization. There is no requirement regarding theparticle diameter of toner. However, from the standpoint of yieldingimages which are excellent in terms of graininess and tone, toner isdesired to be no less than 4 μm and no more than 8 μm in particle size.

(Intermediary Transfer Belt)

As the resinous substances which can be used as the material for thetransfer belt 8 which is endless and circularly movable, just about anyresinous substance is usable, as long as it is thermoplastic andthermally curable. As the thermoplastic resin, polyethyleneterephthalate(PET), polycarbonate (PC), polyamide (PA), polyphenylsulfide (PPS),polyether-sulfon (PES), polyetheretherketon (PEEK), or the like can beused. Further, as the thermally curable resin, polyimide (PI) can beused.

Carbon black and/or metallic particles as an electrically conductivesubstance are mixed into the above-mentioned resinous substance by aproper amount. Then, the mixture is formed into an endless belt. Thefinished belt is 1×10⁹-1×10¹³ Ω·cm in volume resistivity, and1×10⁹-1×10¹³Ω/□ in surface resistivity. This range in resistance is sucha range that a toner image can be preferably transferred.

If the transfer belt 8 is excessively low in electrical resistance, theelectrical charge given to the back surface of the transfer belt 8quickly attenuates, reducing thereby the electrostatic force which keepsthe toner image held to the transfer belt 8, during the transfer(primary) of a toner image from the drum 1 of each image forming portiononto the transfer belt 8. Thus, the toner image is likely to bedisturbed after its transfer onto the intermediary transfer belt 8. Onthe other hand, if the transfer belt 8 is excessively high in electricalresistance, the transfer belt 8 becomes overcharged, increasingtherefore the electrostatic attraction between the drum 1 and transferbelt 8, during the primary transfer. Thus, as a given portion of thetransfer belt 8 separates from the photosensitive drum 1, electricaldischarge occurs between the photosensitive drum 1 and this portion ofthe transfer belt 8, making it likely for the toner image on theintermediary transfer belt 8 to be disturbed.

(Secondary Transfer)

As for the transfer (secondary transfer) of a toner image from thetransfer belt 8 onto a sheet S of recording medium in the secondarytransfer nip 14, the secondary transfer voltage (positive in thisembodiment), which is opposite in polarity to the polarity to whichtoner is charged, is applied to the secondary transfer roller 13 from abias voltage power source 45 which is under the control of the controlportion 200. As a result, the four toner images, different in color, onthe transfer belt 8 are electrostatically transferred together onto thesheet S of recording medium (secondary transfer). The secondary transferroller 13 is synchronously rotated with the transfer belt 8, by thetransfer belt 8 as the transfer belt 8 is rotationally driven. Thebackup roller 9 against which the secondary transfer roller 14 ispressed with the presence of the intermediary transfer belt 8 betweenthe two rollers 14 and 9 is grounded.

The secondary transfer roller 13 is made up of a metallic roller, and anelectrically conductive elastic layer formed on the peripheral surfaceof the metallic roller in a manner to envelop the metallic roller. Asthe material for the elastic layer, a mixture of foamable rubberysubstance such as NBR, urethane, and epichlorohydrin, and anion-conductive agent for adjusting the mixture in electrical resistanceto a value in a range of 1×10⁷-1×10⁹ (Ω). The secondary transfer roller13 is greater in width (dimension in terms of direction perpendicular torecording medium conveyance direction X (direction in which sheet isconveyed)) than the widest sheet S of recording medium which theprinting portion 50 can accommodate.

(Fixing Apparatus)

FIG. 2 is a schematic cross-sectional view of the essential portions ofthe fixing apparatus 16. This fixing apparatus 16 employs a fixationbelt (film), through which a sheet S of recording medium and the tonerimage thereon are heated. It is substantially shorter in the length ofstartup time, and also, substantially smaller in power consumption, thanother types of fixing apparatus, being therefore referred to as OMF(on-demand fixing device). Since this type of fixing apparatus has beenwell-known, it will be only briefly described.

The fixing apparatus 16 has: a fixation belt 18 which is circularlymovable; and an elastic pressure roller 19, which is placed in contactwith the bottom portion of the loop (belt loop) which the fixation belt18 forms. Further, it has a combination of a heater holder 21 and aheater 20 (ceramic heater), which is disposed on the inward side of thefixation belt loop. The heater 20 is attached to the bottom surface ofthe heater holder 21 in a manner to extend in the lengthwise directionof the heater holder 21. The fixing apparatus 16 is structured so thatthe fixation belt 18 is allowed to slide on the heater 20, with theinward surface of the fixation belt 18 remaining in contact with theheating surface of the heater 20. The heater holder 21 is formed ofhighly heat resistant liquid polymer. Not only does it play the role ofholding the heater 20, but also, the role of guiding the fixation belt18.

The lengthwise ends of the heater holder 21 are kept pressed toward theaxial line of the pressure roller 19 by a preset amount of pressureapplied by a pressure applying mechanism 45 (FIG. 6, which does not showstructural details of mechanism) which is under the control of thecontrol portion 200. Thus, the bottom surface (heating surface) of theheater 20 is pressed against the pressure roller 19, with the presenceof the fixation belt 18 between the heater 20 and pressure roller 19, bythe preset amount of pressure, causing therefore, the elastic layer ofthe pressure roller 19 to be compressed against its resiliency.Therefore, a fixing nip N, which has a preset width, in terms of therecording medium conveyance direction X, necessary for image fixation,is formed between the fixation belt 18 and pressure roller 19.

The fixing apparatus 16 is provided with multiple (three, in thisembodiment) temperature sensors 41 a, 41 b, and 41 c (temperaturedetecting means) for detecting the temperature of the top surface of theheater 20. The temperature sensors 41 are distributed across the heater20 in the lengthwise direction (which is perpendicular to the recordingmedium conveyance direction) (FIG. 4). The information regarding thetemperature detected by the temperature sensors 41 a, 41 b, and 41 c isfed back to the control portion 200.

(Fixation Belt)

The fixation belt 18 has a substrative layer, and a surface layer coatedon the outward surface of the substrative layer. The substrative layeris formed of heat resistant resin such as polyimide, polyamide-imide andPEEK (polyether-ether-keton), or metallic substance such as SUS(stainless steel), Al, Ni, Cu and Zn, or their alloy, which is heatresistant and thermally highly conductive. In a case where a resinoussubstance is used as the material for the subsrative layer, particles ofBN, alumina, Al, or the like, which is thermally highly conductive, maybe mixed into the resinous substance to provide the fixation belt 18with superior thermal conductivity. As for the material for the surfacelayer as a release layer which is for preventing toner offset, and/orensuring that a sheet S of recording medium smoothly separates from thefixation belt 18, fluorine resin such as those listed in the nextparagraph, silicone resin, or the like, which is excellent in releaseproperties, and in heat resistance, may be used alone or in mixture.

PTFE (polytetrafluoroethylene)

PFA (tetrafluoroethylene-perfluoroalkylvinyl-ether copolymer)

FEP (tetrafluoroethylene-hexafluoropropylene copolymer)

ETFE (ethylenetetrafluoroethylene copolymer)

CTFE (polychlorotrifluoroethylene)

PVDF (polyvinylidenefluoride), etc.

In this embodiment, PFA was used as the material for the release layer.As for the coating method, the substrative layer may be dipped in thePFA after its outward surface is etched, or the outward surface of thesubstrative layer may be powder-coated. Further, the fixation belt 18may be fitted with a piece of tube made of one of the above-mentionedresins so that the outward surface is covered with the tube. Moreover,the substrative layer may be covered with a release layer formed in theform of a piece of tube in advance, after its outward surface is blastedand coated with adhesive or primer.

The fixation belt 18 in this embodiment has a laminar structure; it hasthree layers. The substrative layer is made of Ni alloy. It is 30 μm inthickness, and 30 mm in internal diameter. The intermediary layer is aresin layer. It is formed on the outward surface of the substrativelayer, of silicone rubber. It is 180 μm in thickness. The outermostlayer is a release layer. It is formed on the outward surface of theintermediary layer, of PFA (PFA tube). It is 30 μm in thickness.

(Pressure Roller)

The pressure roller 19 is an elastic roller. It is made up of a metalliccore 19 a and an elastic layer 19 b. The metallic core 19 a is formed ofa metallic substance such as SUS, SUM (free-cutting steel containingsulphur), and Al. The elastic layer 19 b is formed on the peripheralsurface of the metallic core 19 a, of elastic solid rubber, elasticsponge rubber, foamed elastic rubber, or the like, in a manner toenvelop the metallic core. More specifically, the elastic layer 19 b isa solid rubber layer formed of heat resistant rubber such as siliconerubber and fluorine rubber. Further, in order to make the elastic layer19 b thermally more insulating, the silicone rubber is foamed. Further,hollow fillers (such as micro-balloons) were dispersed in the materialfor the elastic layer to provide the elastic layer with numerous minutegassy hollows, in order to provide the elastic layer with a higher levelof thermally insulating effect.

By the way, the pressure roller 19 may be provided with a release layer,which is formed on the elastic layer 19 b, of PFA resin, PTFE resin, orthe like. In this embodiment, the pressure roller 19 is made up of themetallic core 19 a formed of SUS, and the elastic layer 19 b formed ofelastic solid silicone rubber. It is 25 mm in external diameter.

(Heater)

FIG. 3 is a sectional view of the heater 20 in this embodiment. It showsthe general structure of the heater 20. The heater 20 is made up of asubstrate 22, and a heat generating layers 42 (a and b). The substrate22 is in the form of a piece of plate, which is low in thermal capacity.It is formed of insulative ceramic such as alumina and aluminum nitride.The heat generating layer 42 is formed on the surface of the insulativeceramic substrate 22, of an electrically resistive substance such asAg/Pd (silver-palladium), RuO₂ (Ruthenium oxide), and Ta₂N (Tantalumnitride), which generates heat as electric current is run through it.The heat generating resistor layer 42 is formed by screen printing, andis roughly 10 μm in thickness.

Here, “lengthwise direction” means such a direction that isperpendicular to the direction X in which a sheet S of recording mediumis conveyed. It is parallel to the axial line of the pressure roller 19,and the lengthwise direction of the fixation nip N.

The side of the heater 20, which contacts the inward surface of thefixation belt 18, is covered with a protective layer 23 for protectingthe heat generating resistor layer 42, to a thickness which can hardlyaffect the thermal conductivity between the heater 20 and fixation belt18. The protective layer 23 is desired to be as thin as possible as longas it can provide the heater 20 with satisfactory surface properties. Itis formed of glass, fluorine resin, or the like.

Next, referring to FIG. 4, the method for supplying the heater 20 inthis embodiment with electrical power is described. The fixing apparatus16 in this embodiment is structured so that, in terms of the directionperpendicular to the recording medium conveyance direction X, thecenterline of a sheet S of recording medium coincides with that of therecording medium conveyance passage, regardless of sheet size. 0 in FIG.4 stands for this central referential line (theoretical line). In thisembodiment, the heater 20 is provided with two heat generating resistorlayers 42 a and 42 b, that is, the upstream and downstream ones in termsof the recording medium conveyance direction X. As the first and secondswitches 43 a and 43 b, which are under the control of the controlportion 200, are turned on, the two heat generating layers 42 a and 42 bare made to generate heat by the electrical current flowed through them,by the AC voltage applied thereto from an electrical power source 44 (ACpower source).

The two switches 43 (a and b) are turned on or off at a frequency in arange of several msec-several 100 msec to keep the temperature of theheater 20 at a preset level. More concretely, there are a couple ofmethods for controlling the temperature of the heater 20. One is to turnon the commercial AC voltage during specific periods which correspond tospecific portions of the waveform of the voltage (duty ratio control),and the other is to input a preset number of units (which corresponds tohalf of waveform) of the voltage (wave number control). In thisembodiment, the control method based on duty ratio was employed.

In terms of the lengthwise direction, the heat generating resistorlayers 42 a and 42 b are nonuniform in width, being therefore nonuniformin electrical resistance. More specifically, both the layers 42 a and 42b have the center portion, and end portions. However, the two aredifferent in that, in terms of the recording medium conveyancedirection, the center portion of the layer 42 a is wider than that ofthe layer 42 a, and also, that the end portions of the layer 42 a areshaped so that the closer it is to the center, the wider, beingtherefore smaller in electrical resistance, whereas the end portions ofthe layer 42 b are shaped so that the closer it is to the center, thenarrower, being therefore greater in electrical resistance. In otherwords, the layer 42 a is intended to heat primarily the center portionof the fixation nip N, whereas the layer 42 b is intended to heatprimarily the lengthwise end portions of the fixation nip N, since thenarrower (in terms of left-right direction in FIG. 5) the layer 42, thehigher it is in electrical resistance (top-bottom direction in FIG. 4),being therefore greater in the amount of heat generation (becominghigher in temperature (W=RI²) as long as the electrical currentcontinues to flow in the top-bottom direction.

Here, it is assumed that the duty ratio for driving the heat generatingresistor layer 42 a is Da, and that or heat generating resistor layer 42b is Db. In a case where a sheet S of recording medium is conveyed inthe landscape mode, both Da and Db are set to 70%. In comparison, in acase where the sheet S is conveyed in the portrait mode, Da is set to80%, and Db is set to 20%, making it possible to prevent the lengthwiseend portions, that is, the out-of-sheet-passage portions, of thefixation belt 18 from becoming excessively high in temperature. That is,it is desired to control the frequency with which the heat generatingresistors, with which the heater 20 is provided, are made to generateheat. Conveying a sheet S of recording medium in the landscape mode asshown in FIG. 4 corresponds to the conveyance of the widest sheet ofrecording medium which can be accommodated by the image formingapparatus (fixing apparatus). Conveying a sheet S of recording medium inthe portrait attitude corresponds to the conveyance of the narrowestsheet of recording medium.

(Driving of Fixing Apparatus)

As the driving force from a motor M (driving force source), which isunder the control of the control portion 200, is transmitted to themetallic core 19 a of the pressure roller 19 through a driving forcetransmission mechanism (unshown), the pressure roller 19 is rotationallydriven at a preset peripheral velocity in the counterclockwise directionindicated by an arrow mark R1 in FIG. 2. As the pressure roller 19 isrotationally driven, the fixation belt 18 is rotated in the directionindicated by an arrow mark R18 by the friction which occurs between thefixation belt 18 and pressure roller 19 in the fixation nip N as thepressure roller 19 rotates.

Further, electric power is supplied to the heat generating resistorlayers 42 (a and b) of the heater 20, with the use of the powersupplying method described with reference to FIG. 4. Thus, thetemperature of the heater 20 increases to a preset level (fixationtemperature), and is kept at the preset level. More specifically, thetemperature of the heater 20 is controlled by controlling the amount bywhich electric power is supplied to the heat generating resistor layers42 from the power source 44, based on the information regarding thetemperatures detected by the temperature sensors 41 a, 41 b and 41 c.

While the temperature of the fixing apparatus 16 is kept at the presetfixation level, a sheet S of recording medium, which is bearing anunfixed toner image, is introduced into the fixing apparatus 16, and isconveyed through the fixation nip N while remaining pinched between thefixation belt 18 and pressure roller 19. Thus, the unfixed toner image Ton the sheet S is thermally fixed to the sheet S.

(Image Reading Portion)

FIG. 5 is a schematic sectional view of the image reading portion 51 inthis embodiment. The image reading portion 51 is made up of an imagereading apparatus 101 and an automatic document feeder 102. Theautomatic document feeder 102 has a original feeder tray 104, aconveying portion for conveying sheets of original (document), and adelivery tray 117. An original 103 is placed in the original feeder tray104. Then, it is conveyed from the original feeder tray 104 to aseparating portion (combination of separation pad 107 and separationroller 108) by a pickup roller 106. The combination of the separationpad 107 and separation roller 108 separates the topmost sheet from therest of the sheets in the document tray 103.

The original feeder tray 104 is provided with a pair of lateral plates105 for controlling the lateral movement of the documents (originals).Thus, as originals are placed on the original feeder tray 104, thelateral edges of the originals come into contact with the lateral plates105. Therefore, the originals are prevented from being conveyed askew.After being separated from the rest of sheets in the tray 103, eachoriginal is conveyed to the first pair of registration rollers 109, bywhich it is corrected in attitude if it arrives askew. Then, it isconveyed by a second pair of registration rollers 110, the firstconveyance roller 111, and the second registration roller 112, to aposition in which it is read.

There is disposed an original detection flag 127 of an originaldetection sensor 128, between the first and second conveyance rollers111 and 112. The timing with which reading of the original is to bestarted is controlled based on the result of the detection of the flag127. After being conveyed through the reading position, the original isconveyed further by the third and fourth conveyance rollers 113 and 114,and then, is discharged into the delivery tray 117 by a pair ofdischarge rollers 116.

While an original is moved on the top side of the reading position,which is between the second and third conveyance rollers 112 and 113, itis illuminated by the light projected thereupon from a pair of lightsources 119 and 120. Then, the light reflected by the original goesthrough a plate 118 of glass (glass platen), is deflected by mirrors121, 122 and 123, and is guided to a focal lens 124, by which it is madeto converge on a line sensor 125 made up of photoelectric elementsarranged in a straight line. Then, the light is converted into anelectrical signal by the line sensor 125, and then, is converted into adigital signal by a signal processing circuit 125.

(Control Portion)

FIG. 6 is a block diagram of the control system. The control portion 200has a general control portion 201, a printer controlling portion 203, animage processing portion 204, a signal processing circuit 126, and anoriginal reading portion controlling portion 205.

General control portion 201 is provided with a CPU 206, and integrallycontrols a control panel 201 (user interface), the printer controllingportion 203, and the original reading portion controlling portion 205.The printer controlling portion 203 is in connection to various portionsof the printing portion 50, which need to be controlled. FIG. 6 showsonly the fixing apparatus 16 of the image forming apparatus, among thevarious portions which are in connection to the control portion 200. Theoriginal reading portion controlling portion 205 is in connection tovarious portions of the original reading portion 51, which need to bedriven and controlled. FIG. 6 shows only the signal processing circuit126, among various portions of the original reading portion 51.

(Portions of Image Heating Apparatus, which Characterizes thisEmbodiment)

In this embodiment, sheets S of recording medium, which are unusuallyshaped (nonrectangular sheet which results as box is unfolded on flatsurface) as shown on the right-hand side of FIG. 7, for example, areread in advance by the original reading portion 51, and their shape, andthen, are placed in the recording medium holding portion 100. Then, theimage formation process (image formation condition) of the printingportion 50 is controlled according to the shape of each sheet ofrecording medium. Thus, it is possible to obtain high quality products(prints) regardless of the shape of the sheet of recording medium. Bythe way, in order to describe the positional relationship between asheet S of recording medium and heater 20 in terms of its widthwisedirection, a schematic drawing of the heater 200 was added to the leftportion of FIG. 7.

FIG. 8 is a flowchart of the operational sequence of the CPU 206 of thegeneral control portion 201 of the control portion 200 which controlsthe image forming apparatus in this embodiment.

1) In a case where a user wants to print an image on an unusually shapedsheet of recording medium such as the one shown on the right portion ofFIG. 7, the user is to select a “unusually shaped recording mediumprinting mode” from the main menu (unshown) on the screen (liquidcrystal tough panel) of the control panel 202. As this printing mode isselected, the CPU 206 displays a combination of a button 251 for“unusually shaped material printing mode” and a cancel button, on thescreen 202B, as shown in part (a) of FIG. 9 (Step S101).

2) As the user presses the button 251 (Step S102), the CPU 206 displaysa combination of an instruction (prompt), and a reading start button252, and a cancel button, such as the one shown in part (b) of FIG. 9 onthe display screen 202B (Step S103). That is, the CPU displays thecombination of the instruction “Scan material shape. Place material on apreset area of auto document feeder 1 (which hereafter will beabbreviated as “feeder”), in such attitude that surface having an imageto be printed facing upward” the reading start button 252, and thecancel button (Step S103).

The user is to follow the instruction; the user is to set an unusuallyshaped sheet S of recording medium, that is, the unusually shapedmaterial shown in FIG. 7, on the area of the feeder 102, where theoriginal 103 is in FIG. 5.

If multiple unusually shaped sheets S of recording medium are the samein shape, the operator has to set only one of them. In a case wheremultiple groups of sheets S of recording medium are used, and each groupis made up of multiple sheets which are different in shape, the user hasto set only one group. In a case where multiple sheets of recordingmedium, which are different in shape, are used, all the sheets S have tobe individually set. The CPU 206 confirms whether or not the sheets ofrecording medium have been set on the feeder 102, with the use of adetecting means (unshown) (Step S104).

3) Next, the user is to press the “reading start” button 252 (StepS105). As the user presses the button 251, the CPU 206 activates thefeeder 102 by way of the original reading portion controlling portion205 (Step S106). Thus, the sheet S of recording medium sent from thefeeder 102 begins to be scanned (read) by the image reading apparatus101. By the way, if the CPU 206 cannot confirm the setting of the sheetsS on the feeder 102, it does not activate the feeder 102.

The image (1) (first information of image) of the sheet S of recordingmedium scanned by the image reading apparatus 101 is sent to the imageprocessing portion 204 (Step S107). The image processing portion 204extracts the image (2) (second information of image), that is, edgecomponents of the image (1) (Step S108). Further, the image processingportion 204 extracts from the image (2), the information regarding theshape of the sheet S (Step S109), and transmits the information to theprinter controlling portion 203 (Step S110).

In this embodiment, a sheet of recording medium, on which a toner imageis to be formed, is set in the original reading portion 51, and is readto obtain the second information (of sheet), before a toner image isformed on the sheet. Then, the image processing portion 204 obtains theinformation regarding the shape of the sheet S by processing the secondinformation. That is, the image processing portion 204 is the means forprocessing the second information to obtain the shape of the sheet S.

4) Next, the CPU 206 displays a message “information regarding shape ofmaterial has been obtained”, and an image formation start button 253, onthe screen (Step S111).

In a case where a sheet S of recording medium set in Step S103 is toothick and/or too rigid to be moved through the feeder 102, the followingprocedure is to be followed. That is, the user is to lift the feeder102, and place each sheet S on the glass platen 118, so that the sheet Scan be individually scanned. In such a case, the combination of thelight sources 119 and 120, mirrors 121, 122 and 123, focal lens 124,line sensor 125 is moved in the crosswise direction of the drawing toscan the sheet S.

As the user presses the print start button 253 (Step S112), the CPU 206displays a combination of an instruction, an “OK” button 254, and acancel button, on the screen 202B, as shown in part (d) of FIG. 9 (StepS113). More specifically, it displays the combination of the instruction“Rotate scanned material by 180

, turn the material upside down, and place the material in the recordingmedium holding portion so that the surface of the material, on which animage is to be formed, faces upward” and OK button 254, and cancelbutton. Since the scanned sheet S is in the delivery tray 117 or on theglass platen 118, with its surface, on which an image is to be formed,facing downward, the operator is to follow the instruction displayed onthe screen 202 to make the surface of the sheet S, on which an image isto be formed, face upward.

5) As the user places the sheet S in the recording medium holdingportion 10 as instructed, and presses the OK button 254 (Step S114), theCPU 206 displays a combination of an instruction, a start reading button255, and a cancel button, such as the one shown in part (e) of FIG. 9,on the screen 202B. That is, the CPU displays the combination of aninstruction “Scan image to be printed”, a print count window, the startreading button 255, and a cancel button (Step S115).

The user is to set the original 103 to be copied, and input the desiredprint count with the use of the inputting portion 202A. As the userinput the desired print count, the value of the input count is displayedin the print count window. Then, the user is to press the start readingbutton 255 (Step S116). Then, the CPU 206 activates the feeder 102,causing thereby the image reading apparatus 101 to begin scanning(reading) the original sent thereto by the feeder 102. Then, the image(3) of the original, which was obtained by the image reading apparatus101 through the process of scanning the original, is sent to the imageprocessing portion 204 (Step S118).

The image processing portion 204 has the information regarding the shapeof the sheet S of recording medium which was scanned in Step S107, inits memory (unshown). Thus, it processes the image (3) according to theshape of the sheet S (to provide margins, or the like), and sends theresults of the processing to the printer controlling portion 203 (StepS119).

6) As soon as Step S119 is completed, the CPU 206 makes the printingportion 50 begin to operate (Step S120) to form a toner image on thetransfer belt 8 through the processes such as those described above. Assoon as the toner image is formed on the transfer belt 8, a sheet of Sof recording medium is conveyed to the secondary transferring nip 14with preset timing. To the secondary transfer roller 13, constantcurrent bias, that is, bias which is stable in current value, is appliedfrom a power source 46 (FIG. 1). The reason why bias is applied toprovide constant current is to ensure that the electrical force fortransferring a toner image T onto a sheet S of recording medium remainsstable even if the transfer belt 8 and secondary transfer roller 13reduce in electrical resistance due to their repeated usage.

The printer controlling portion 203 controls the amount by whichelectrical current is flowed to the secondary transfer roller 13 fromthe power source 46, in synchronism with the progression of the passageof a sheet S of recording medium through the secondary transfer nip 14,as shown in FIG. 10. That is, while the portion of the sheet S, which isnarrower than the other portions of the sheet S, moves through thesecondary transfer nip 14, the printer controlling portion 203 reducesthe current value to 15 μA, whereas while the portion of the sheet S,which is wider than the other portions of the sheet S, moves through thesecondary transfer nip 14, the printer controlling portion 203 keeps thecurrent value greater at 20 μA.

Thus, it is possible to prevent the following problem; as the portion ofa sheet S of recording medium, which is narrower (in terms of verticaldirection in FIG. 10) than the other portions of the sheet S, isconveyed through the secondary transfer nip 14, the electric currentbecomes excessive, and therefore, the toner image T is disturbed by theelectrical discharge triggered by the excessive amount of current. It isalso possible to prevent the problem that while the portion of the sheetS, which is wider than the other portions of the sheet S, is conveyedthrough the secondary transfer nip 14, the toner image T fails totransfer onto the sheet S because of the insufficiency in the amount ofelectric current. That is, because the printer controlling portion 203controls the power source 46 in the amount of electric current flowed bythe power source 46, the toner image T is transferred onto a sheet S ofrecording medium by a proper amount of electric current, even if thesheet S is unusual in shape.

At the same time as the printer controlling portion 203 activates theprinting portion 50 in Step S120, it sets the duty ratio Da for the heatgenerating resistor layer 42 a of the fixing apparatus 16 to 60%.Further, it sets the duty ratio Db for the heat generating resistorlayer 42 b to 45%.

These settings are decided based on the information regarding the shapeof a sheet S of recording medium. That is, when the ratio of the portionof the sheet S, which is being moved through the secondary transfer nip14, to the width of the heat generating resistor layers 42, in terms ofthe lengthwise direction of the secondary transfer nip 14, is small, asmaller amount of heat is given to the secondary transfer nip 14,whereas when the ratio is larger, a larger amount of heat is given. Withthe use of this control, even if a sheet S of recording medium, on whicha toner image T is to be formed, is unusual in shape, it is uniformlyheated, and therefore, it is possible to prevent the problem that as atoner image T is conveyed through the fixation nip N, it becomesnonuniform in gloss due to the nonuniformity in the amount of heat giventhereto.

Further, the printer controlling portion 203 changes the amount by whichpressure is applied to the fixation nip N by the pressure applyingmechanism 45 (FIG. 6), in synchronism with the timing with which anunusually shaped sheet S of recording medium is conveyed through thefixation nip N, as shown in FIG. 11. More concretely, while the narrowportion of the sheet S moves through the fixation nip N, the printercontrolling portion 203 keeps the amount of pressure at 240 N, whereaswhile the wider portion of the sheet S moves through the fixation nip N,the printer controlling portion 203 keeps the amount of pressure at 300N. Thus, even if an unusually shaped sheet S of recording medium isconveyed through the fixation nip N, the pressure applied to the sheet Sremains stable. Therefore, it is possible to prevent the problem that atoner image T becomes nonuniform in gloss due to the nonuniformity inthe pressure between the sheet S (toner image T) and fixation belt 18.

As described above, if the image processing portion 204, as the meansfor processing the information regarding the shape of a sheet ofrecording medium, detects that the sheet S is not in an ordinaryrectangular shape, the printer controlling portion 203 controls theimage forming apparatus in the following manner; it changes the presetamount by which voltage is applied to the secondary transfer roller 13,preset amount by which current is flowed through the secondary transferroller 13, preset amount by which a combination of heat and pressure,heat, or pressure is applied to the fixation nip N, according to theinformation regarding the detected shape of the sheet S. Therefore, evenwhen a sheet of recording medium, which does not have an ordinaryrectangular shape, is used as recording medium, it is possible to easilyset proper transfer conditions and/or fixation conditions.

The printer controlling portion 203 controls the heater 20 of the fixingapparatus 16 in heat distribution, in terms of the direction which isperpendicular to the recording medium conveyance direction, based on theinformation regarding the aforementioned detected shape of the sheet Sof recording medium, in order to properly set fixation conditions foreach of various sheets S of recording medium which are different inshape, thickness, and/or the like property. The printer controllingportion 203 controls the heater 20 in the above-mentioned heatdistribution, by controlling the power supply to the heat generatingresistor layers 24 (a and b), which the fixing apparatus 16 posses. Thefixing apparatus 16 is provided with multiple (three in this embodiment)temperature detecting means 41 (a-c), which are different in position interms of the direction perpendicular to the recording medium conveyancedirection X. The printer controlling portion 203 controls the heater 20in the heat distribution with the use of at least one of thesetemperature detecting means 41.

7) As soon as the image formation on a preset number of sheets S ofrecording medium is completed, the CPU 206 stops the image formingapparatus (End).

Through the operational steps described above, the fixation conditionscan be easily set even for sheets of recording medium which are not inthe form of an ordinary rectangular shape.

Embodiment 2

The image forming apparatus in this embodiment is roughly the same asthe one in the first embodiment, except for the following features whichcharacterizes the apparatus. FIG. 12 is a top view of the fixingapparatus 16 in this embodiment. It does not show the nonessentialcomponents of the fixing apparatus 16. The heat distribution of thefixation belt 18 in terms of its widthwise direction (lengthwisedirection) is detected by the temperature detecting means 41 a, 41 b,and 41 c. It is based on the results of the detection of this heatdistribution that the printer controlling portion 203 controls thefixing apparatus 16, in particular, in the duty ratios Da and Db.

There is disposed three cooling fans (cooling means), which are underthe control of the control portion 200, in the adjacencies of the centerportion and lengthwise end portions of fixation belt 18, one for one, interms of the widthwise direction of the belt 18.

The printer controlling portion 203 adjusts the power supply in the dutyratio Da and Db in order to deal with various sheets S of recordingmedium, which are different in shape. However, if it determines that theadjustment in the duty ratios Da and Db is failing to keep thetemperature distribution of the heater 20 in a preset range in terms ofthe widthwise direction of the fixation belt 18, it cools the fixationbelt 18 with the use of the fans Fa, Fb and Fc.

For example, if it is detected by the temperature detecting means 41 a,41 b and 41 c that the lengthwise end portions (top and bottom portionsin FIG. 12) of the fixation belt 18 are higher than a desired level, theprinter controlling portion 203 activates the fans Fa and Fb, which arein the adjacencies of the lengthwise end portions of the fixation belt18, to cool the lengthwise end portions of the fixation belt 18.Further, if a sheet S of recording medium, such as the one shown in FIG.12, which has a hole Sa in the center, is used as the recording medium,the printer controlling portion 203 sets the duty ratios Da and Db to50% and 70%, respectively, and drives the fan Fb.

Also in this embodiment, the printer controlling portion 203 controlsthe heater 20 of the fixing apparatus 16, in the heat distribution interms of the direction perpendicular to the recording medium conveyancedirection X, according to the information regarding the detected shapeof a sheet S of recording medium. More specifically, the printercontrolling portion 203 controls the above-mentioned heat distribution,by controlling the power supply to the heat generating resistors 42 (aand b) which the fixing apparatus 16 has. Further, the printercontrolling portion 203 controls the above-mentioned heat distributionalso by controlling the cooling means F (a-c) which the fixing apparatus16 has.

The fixing apparatus 16 is provided with multiple (three in thisembodiment) temperature detecting means 41 (a-c), which are different inposition in terms of the direction perpendicular to the recording mediumconveyance direction X. The printer controlling portion 203 controls theheater 20 in the heat distribution with the use of at least one of thesetemperature detecting means 41.

Therefore, the fixation conditions can be easily set even for sheets ofrecording medium which are not in the form of an ordinary rectangularshape.

Embodiment 3

The image forming apparatus in this embodiment is also roughly the sameas the one in the first embodiment. However, it is different inoperation from the one in the first embodiment. Thus, the operation ofthis image forming apparatus is described with reference to a case inwhich a recording medium such as an envelope shown in FIG. 13, which hasareas having two-five layers of recording medium (paper), is used inplace of an ordinary sheet S of recording medium, is described. Theportion of an envelope, which has two layers of paper (recordingmedium), and the portions the envelope, which has five layers of paper(recording medium), are substantially different in thickness. Therefore,a substantial step is present between the two portions. Thus, if imagesare formed on a large number of envelops or the like, the components ofthe fixing apparatus 16, which are in the adjacencies of the secondarytransfer nip 14, and also, in the adjacencies of the fixation nip N,wear faster across the portions which correspond to where five layers ofrecording medium (paper) overlap, than other parts of the envelope. Thishas been the reason why the fixation belt 18, pressure roller 19, etc.,of the fixing apparatus 16 had to be replaced more frequently ifenvelops or the like were used as recording medium than when ordinarysheets of recording medium were used.

FIG. 14 is a flowchart of the control sequence of the CPU 206 of thegeneral control portion 200 which controls the image forming apparatusin this embodiment.

1) When a user wants to use envelops as recording medium, the user is toselect the “envelop printing mode” from the main menu (unshown) on thescreen (liquid crystal touch screen) of the control panel 202. As the“envelop printing mode” is selected, the CPU 206 displays a combinationof an “envelop printing mode” selection button 256 and an envelopeprinting mode cancel button on the screen 202B (Step S201), as shown in(a) of FIG. 15.

2) As the user presses the button 256 (Step S202), the CPU 206 displaysa combination of an instruction, a reading start OK button 267, and acancel button, such as the one shown in part (b) of FIG. 15, on thescreen 202B. That is, the CPU 206 displays the combination of theinstruction “Scan envelop for its shape. Pick one envelop, and place iton preset position on auto document feeder 102, in such attitude thatside (back surface) having overlapping portion facing upward”, a readingstart button 257, and cancel button, on the screen 202B

(Step S203).

As the user sets a recording medium S, which is an envelop, on theportion of the feeder 102, where the original 103 is in FIG. 5,following the instruction, the CPU 206 confirms whether or not therecording medium S is in the feeder 102 with the use of a detectingmeans (unshown) (Step S204). It is assumed here that the multiplerecording mediums S (envelops) are the same.

3) Then, the user is to press the “start reading” button 257 (StepS205). As the user presses the button 257, the CPU 206 activates thefeeder 102 by way of the original reading portion controlling portion205 (Step S206). Thus, the recording medium S fed by the feeder 102 isscanned (read) by the image reading apparatus 101. By the way, if theCPU 206 cannot confirm that the recording medium S has been set in thefeeder 102, it does not activate the feeder 102.

The image (2) of the recording medium S obtained by the scanning of therecording medium S by the image reading apparatus 101 is sent to theimage processing portion 204 (Step S207). The image processing portion204 makes the image (12) of the contour of the recording medium S fromthe image (2) by extracting the edge component of the image (2) (StepS208), and obtains the information regarding the shape of the recordingmedium S from the image (12) (Step S209). Then, it sends the informationto the printer controlling portion 203 (Step S210). This informationregarding the shape of the recording medium S includes the informationregarding the border lines between the two layer portions of the envelopand the other portions, which are indicated by solid lines in FIG. 13,in addition to the information regarding the contour of the envelop.

The CPU 206 determines which of the commercially available envelops therecording medium S is, with reference to the data base stored in amemory (unshown) (Step S211). It uses also the information regarding theborder among the areas of the envelope, where the envelop material(paper) overlaps.

4) Thereafter, the CPU 206 displays a combination of a message “Envelopeshape was obtained”, a print start button 258, and a cancel button, onthe screen 206B, as shown in part (c) of FIG. 15 (Step S212).

The recording medium S, which is the envelope fed into the image readingapparatus 101 and scanned by the apparatus 101, is in the delivery tray117, with its multilayered portions facing downward. By the way, in acase where the recording medium S, which is an envelop, is such arecoding medium that is impossible to be fed into the image readingapparatus 101 by the feeder 102, it has only to be manually placed onthe glass platen 118 to be scanned. In such a case, the recording mediumS is placed on the glass platen 118 in such an attitude that its addressplacement surface faces upward, and its multilayer portions facingdownward.

As the user presses the printing start button (Step S213), the CPU 206displays a combination of a question and three buttons such as thoseshown in part (d) of FIG. 15, on the screen 206B (Step S214). That is,it displays the combination of the question “which side of recordingmedium”, an address side button 259, a backside button 260, and a cancelbutton.

5) As the user presses the address side button 259, the CPU 206determines in Step S215 that the answer is Y, and displays aninstruction “Place envelop in recording medium holding portion withoutchanging envelop in attitude” on the screen 202B, as shown in part (e)of FIG. 15 (Step S216).

If the user presses a back-side button 260, the CPU 206 determines inStep S125 that the answer is N, and displays an instruction “Takeenvelop out, turn envelop 180° without turning it upside down, and placeenvelop in recording medium holding portion” on the screen 202B as shownin part (f) of FIG. 15 (Step S217).

In Step S216 or S217, a set completion button 261 or a cancel button 262is pressed by the user. The CPU 206 displays a combination of aninstruction “Transmit printing job”, an OK button 263, and a cancelbutton, on the screen 202B as shown in part (g) of FIG. 15 (Step S218).

The user is to press the OK button 263 to initiate the transmission ofthe printing job. As the OK button 263 is pressed, the general controlportion 201 puts the printing portion 50 on standby (Step S219), andreceives, as an external input, the printing job which the usertransmitted by operating the external apparatus 300 such as a computer(Step S220). As the general control portion 201 receives the printingjob, it communicates with the printer controlling portion 203, andstarts a printing operation (Step S221).

6) FIG. 16 is a flowchart of the subordinate sequence in Step S221 to becarried out by the printer controlling portion 203. It is for describingin detail, Step S221 which characterizes this embodiment.

The printer controlling portion 203 receives the information regardingthe print count (integer) of the printing job from the general controlportion 201 (Step S301). Then, it determines whether or not the printcount is no more than 100 (Step S302). If the user chooses Y in StepS302, the printer controlling portion 203 prints the desired image onthe selected recording medium until the desired number (no more than100) of product are outputted (Step S303), and ends the printingoperation. If the answer in Step S302 is N, the printer controllingportion 203 outputs the first 100 products, and deducts 100 from thedesired print count (Step S304). Then, it communicates with the imageprocessing portion 204 by way of the general control portion 201, andhorizontally turns by 180 degrees the image to be written (Step S305).

Next, the CPU 206 displays a combination of an instruction “Take envelopout, horizontally rotates it by 180°, and reset envelop”, a settingcompletion button 264, and a cancel button, on the screen 202B, as shownin part (h) of FIG. 15 (Step S306). If the user presses the “settingcompletion” button 264 (Step S307), the CPU 206 returns to Step S302.

By following the subordinate sequence described above, the user canplace the envelops in the feeder 102 in such a manner that themultilayered portion of the envelop is alternately placed on the leftand right sides of the feeder 102. Thus, it is possible to prevent theproblem that certain portions of the transfer belt 8, secondary transferroller 13, backup roller 9, fixation belt 18, pressure roller 19, etc.,are subjected to an excessive amount of load. Therefore, it is possibleto extend the life expectancy of these components.

In this embodiment, the above-mentioned effect was obtained by rotatingan envelope. However, the same effect can also be obtained by displacingan envelop in the widthwise direction relative to the recording mediumholding portion 10.

The structure of the image forming apparatus in this embodiment can besummarized as follows. The image forming apparatus is provided with therecording medium holding portion 10 for supplying the transferring meanswith recording mediums, and the screen 202B for giving to the user aninstruction about how recording mediums are to be set in the recordingmedium holding portion 10.

In a case where the printer controlling portion 203 determines, based onthe information from the image processing portion 204 as a shapeinformation processing means, that recording mediums are envelops, theprinter controlling portion 203 displays the following message on thescreen 202B, based on the multilayered area count. That is, the messageis for preventing the problem that envelops are set in the recordingmedium holding portion 10 in such a manner that all the multilayeredportions vertically align on a single spot, in terms of the directionperpendicular to the direction in which recoding medium is conveyed inthe transferring means and/or fixing means. More concretely, the printercontrolling portion 203 displays a message that instructs the user tochange recording mediums (envelops) in orientation and/or positionrelative to the recording medium holding portion 10, in terms of therecording medium conveyance direction X.

By following this message, it is possible to obtain an additionaleffect, that is, an effect that various members of the transferringmeans, and those of the fixing means, can be extended in the intervalwith which they need to be replaced.

Embodiment 4

The user is allowed to input into the control portion 200, theinformation regarding the specification of recording medium S to beused, by way of the control panel 202 and external device 300. In such acase, the control panel 202 and external device 300 are means throughwhich the control portion 200 obtains the specification of the recordingmedium. Further, the recording medium passage from the recording mediumholding portion 10 to the secondary transfer nip N is provided with themeans (unshown) for obtaining the specifications (thickness, basisweight, etc.). The detected information is inputted into the controlportion 200. Therefore, the control portion 200 in the first to thirdembodiment can control the printing portion 50 in the image formationconditions, based on both the specification (thickness, basis weight)and shape of the recording medium to be used for image formation.

The characteristic structural feature of the image forming apparatusesin the first to fourth embodiments can be summarized as follows. Theimage forming apparatuses have: the image forming means 50 for formingan image on a sheet S of recording medium; the reading means 51 forreading the shape of the sheet S on which an image is to be formed; andcontrolling means 200 which controls the image formation conditions forthe image forming means 50, based on the shape of the sheet S obtainedby the reading means 51.

The image forming means 50 has the transferring means 13 which transfersthe image formed on the image bearing member 8, onto the sheet S. Theimage formation conditions which the controlling means 200 controls arethe transfer conditions for the transferring means 13. The image formingmeans 50 has the fixing means 16 which fixes the image formed on thesheet S. The image formation conditions which the controlling means 200controls are the fixation conditions for the fixing means 16. Thereading means 51 has also the function of reading the original. It has ameans for obtaining the specification (basis weight) of the sheet S. Thecontrol portion 200 controls the image formation conditions based onboth the shape and specification of the sheet S.

Each of the above-mentioned image forming apparatuses has: the recordingmedium holding portion 10 in which the sheet S is set; image formingmeans 50 which forms an image on the sheet S conveyed from the recordingmedium holding portion 10; and reading means 51 which reads the shape ofthe sheet S on which an image is to be formed. Further, it has theinforming means 202B (screen), on which the method for setting the sheetS in the recording medium holding portion 10 according to the shape ofthe sheet S obtained by the reading means 51 is displayed. The readingmeans 51 has also the function of reading an original. The controllingmeans 200 has a means for obtaining the specification (basis weight) ofthe sheet S, and controls the image formation conditions, based on boththe shape and specification of the sheet S.

(Miscellanies)

(1) The image bearing member onto which a toner image is transferred isnot limited to an image bearing member, onto which a toner image istransferred from the first image bearing member. It may be such a memberas an electrophotographic photosensitive member, an electrostaticallyrecordable dielectric member, and a magnetically recordable magneticmember, on which a latent image can be formed, be developed into a tonerimage with the use of developer, and from which the formed toner imagecan be transferred onto the final recording medium.

(2) An image forming apparatus with which the present invention iscompatible is not limited to a full-color image forming apparatus suchas those in the preceding embodiments. That is, the present invention isalso compatible with an image forming apparatus for forming amonochromatic image. Further, an image forming method with which thepresent invention is compatible is not limited to an electrophotographicmethod. That is, the present invention is also compatible with an imageforming apparatus of the so-called transfer type, which uses a recordingmethod other than an electrophotographic method. For example, thepresent invention is also compatible with an image forming apparatus ofthe so-called transfer type, which forms a toner image with the use ofan electrostatic recording method, a magnetic recording method, or thelike.

(3) A fixing apparatus to which the present invention is applicable isnot limited to such a fixing apparatus as the fixing apparatus 16 in thepreceding embodiment which fixes a toner image to recording medium withthe use of a combination of heat and pressure. That is, the presentinvention is also applicable to an apparatus which fixes a toner imagewith the use of heat or pressure.

(4) In the preceding embodiments, the fixing apparatus 16 was anapparatus for fixing an unfixed toner image T formed on recordingmedium, by heating the toner image T. However, these embodiments are notintended to limit the present invention in scope in terms of the type offixing apparatus to which the present invention is applicable. Forexample, the present invention is also applicable to an apparatus forreheating a toner image which has been temporarily fixed to recordingmedium, to increase the toner image in glossiness (this type ofapparatus also is referred to as fixing apparatus).

(5) The heating member for heating a rotational member for heating atoner image formed on recording medium, which is compatible with thepresent invention, is not limited to the ceramic heater 20. That is, thepresent invention is also applicable to a fixing apparatus structured toemploy a heating means based on electromagnetic induction, a halogenheater, an infrared lamp, a nickel-chrome wire heater, or the like ofthe internal or external type. Further, the present invention can alsobe applicable to apparatuses structured so that their pressure roller 19is provided with a heating member for heating the pressure roller 19.

(6) Moreover, the present invention is also applicable to a fixingapparatus which has a pair of rotational members 18 and 19 for formingthe fixation nip N, one of which is an endless belt, and the other ofwhich is a roller, or both of which are endless belts or rollers.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2017-062720 filed on Mar. 28, 2017, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. An image forming apparatus comprising: a readingportion configured to read a shape of a first sheet, said readingportion having a function of reading a second sheet carrying an originalimage; an image forming portion configured to form a toner imagecorresponding to the original image read by said reading portion; afixing portion configured to fix the toner image formed by said imageforming portion; and a controller configured to control a fixingcondition of said fixing portion in accordance with the shape of thefirst sheet read by said reading portion.
 2. An apparatus according toclaim 1, wherein the fixing condition is controlled on the basis ofinformation determined on the basis of the shape of the first sheet readby said reading portion correspondingly to a width size of the firstsheet.
 3. An apparatus according to claim 1, wherein said readingportion reads the shape of the first sheet in response to input ofinformation corresponding to a first instruction for reading the firstsheet having a non-rectangular shape, and reads the second sheetcarrying the original image in response to input of informationcorresponding to a second instruction for reading the original image. 4.An apparatus according to claim 1, further comprising an acquiringportion configured to acquire information corresponding to a kind of thesheet, wherein said controller controls the fixing condition on thebasis both of the shape and the kind of the sheet.
 5. An apparatusaccording to claim 4, wherein the kind of the sheet represents a basisweight of the sheet.
 6. An apparatus according to claim 1, wherein saidfixing portion includes a first rotatable member and a second rotatablemember which a cooperative to form a nip configured to heat the imageformed on the sheet by said image forming portion, and wherein saidcontroller controls on temperature of said first rotatable member inaccordance with the shape of the sheet read by said reading portion. 7.An image forming apparatus comprising: a receiving portion configured toreceive information corresponding to an original image from an externalterminal outside of said image forming apparatus; an image formingportion configured to form a toner image corresponding to theinformation received by said receiving portion; a fixing portionconfigured to fix the toner image formed by image forming portion; areading portion configured to read a shape of the sheet on which thetoner image corresponding to the information is formed by said imageforming portion; and a controller configured to control a fixingcondition of said fixing portion in response to a shape of the sheetread by said reading portion.
 8. An apparatus according to claim 7,wherein said controller controls the fixing condition on the basis ofinformation which is determined on the basis of the shape of the sheetread by said reading portion and which response to difference betweenwidths of the sheet.
 9. An apparatus according to claim 7, wherein saidfixing portion includes a first rotatable member and a second rotatablemember which a cooperative to form a nip for hitting the image formed onthe sheet by said image forming portion, and wherein said controllercontrols on temperature of said first rotatable member in accordancewith the shape of the sheet read by said reading portion.